1. Field of the Invention
The present invention relates to an electrophoretic display device, and more particularly, to a method for manufacturing an electrophoretic display device that improves manufacturing efficiency and driving reliability.
2. Discussion of the Related Art
An electrophoretic display device is a display device for displaying images by the electrophoresist phenomenon where colored charged particles move by an externally-applied electric field. In accordance with the electrophoresist phenomenon, when the electric field is applied to electrophoretic dispersion liquid (e-ink) obtained by dispersing charged particles in liquid, the charged particles move in the liquid by the Coulomb force.
Due to bistability of the electrophoretic display device, even though the applied voltage is removed from the electrophoretic display device, the displayed image is maintained for a long time. That is, even though there is no continuous supply of the voltage to the electrophoretic display device, the displayed image can be maintained for a long time. In this respect, the electrophoretic display device is especially appropriate for the electronic book (e-book) which does not require a rapid image stream.
Unlike a liquid crystal display device, the electrophoretic display device has no dependence on viewing angle. In addition, the electrophoretic display device can provide images having sufficient quality to make a user feel comfortable without eye strain. That is, the electrophoretic display device provides paper-like viewing comfort. Furthermore, a demand for the electrophoretic display device is gradually increased due to advantages of flexibility, low-power consumption, and eco-friendly properties.
FIG. 1 is a cross section view illustrating a related art electrophoretic display device.
With reference to FIG. 1, the related art electrophoretic display device includes lower and upper substrates 10 and 20 which are bonded to each facing each other, and an electrophoretic film 30 interposed between the lower and upper substrates 10 and 20. On the lower substrate 10, there are a plurality of pixel electrodes (not shown) which face with a common electrode 22 on the upper substrate 20, and a plurality of thin film transistors (TFTs, not shown) which serve as switching elements to apply a voltage to the plurality of pixel electrodes. The electrophoretic film 30 includes a plurality of microcapsules 32 comprising charged particles and solvent, and an adhesive layer 34 (or passivation layer) for protecting the microcapsules 32 and providing adhesion with the lower substrate 10. Upper substrate 20, the common electrode 22, and the electrophoretic film 30 may be integrated as one body. The microcapsule 32 includes positive (+) charged particles, negative (−) charged particles, and a solvent covering and protecting the charged particles. When an electric field is formed between the pixel electrode of the lower substrate 10 and the common electrode 22 of the upper substrate 20, the charged particles included in the microcapsule 32 move by electrophoresis, thereby displaying images.
For manufacturing the related art electrophoretic display device, the lower substrate 10, upper substrate 20, and lamination electrophoretic film 30 are separately manufactured. Then, the electrophoretic film 30 is interposed between the lower and upper substrates 10 and 20.
As the electrophoretic film 30 is maintained and transported while being provided with a release film (not shown) adhered to the passivation layer 34, the release film must be released from the electrophoretic film 30 just before laminating the electrophoretic film 30 on the lower substrate 10. After that, the passivation film 34 is adhered to the upper substrate 20 by the laminating process.
The respective processes for individually manufacturing the lower substrate 10, upper substrate 20, and electrophoretic film 30 may cause the complexity and the increase of manufacturing time, thereby deteriorating the efficiency. Also, the individually-manufactured electrophoretic film 30 has to be interposed by the additional process, thereby resulting in the increased manufacturing cost.
To overcome these problems, the electrophoretic film may be provided inside the lower substrate 10. However, the solvent may volatilize due to filling time of the electrophoretic dispersion liquid comprising the charged particles and solvent and waiting time of the process for bonding the lower and upper substrates to each other. As the solvent volatilizes due to the filling time of the electrophoretic dispersion liquid comprising the charged particles and solvent, and the waiting time of the process for bonding the lower and upper substrates to each other, the charged particles are not driven normally.
When trying to display full-color images by the electrophoretic display device, the charged particles colored in the specific color overflow into the neighboring pixel with the other-colored charged particles so that the color images are not properly displayed. Especially, if the pixels are filled with the electrophoretic dispersion liquid while being classified in respective colors to realize full-color images, the initially-filled electrophoretic dispersion liquid is different in degree of volatilization from the terminally-filled electrophoretic dispersion liquid. Accordingly, the respective pixels have different driving efficiencies due to the difference in degree of volatilization.
As a result, the pixels are driven abnormally so that the picture quality is deteriorated. If a large amount of the solvent in the electrophoretic dispersion liquid is volatilized, it is impossible to drive the corresponding pixel. Due to the above problems, the picture quality of the electrophoretic display device is deteriorated, thereby resulting in the deteriorated efficiency and reliability.